Interpretive Summary: This research was conducted to test the feasibility of employing juvenile wood acquired from Paulownia trees as bio-filler in thermoplastics. Rapidly growing woody biomass trees offer a huge unexploited source of biofuels, bio-fillers, foods, and chemicals that can be grown on marginal lands. Wood plastic composites (WPC) produce useful products with less petroleum consumption by substitution with bio-based wood. We demonstrated that Paulownia wood flour can be employed as a bio-filler with high density polyethylene to create a WPC. Materials made with these WPCs can be substituted for purely petroleum-based items.

Technical Abstract:
Paulownia wood flour (PWF), a byproduct of milling lumber, was employed as a bio-filler and blended with high density polyethylene (HDPE) via extrusion. Paulownia wood (PW) shavings were milled through a 1-mm screen then separated via shaking into various particle fractions using sieves (#30 - < #200 U.S. Standards). In addition, PWF was also ball ground (BG) for 72 hrs to obtain a fine powder for testing. To determine the influence of coupling agent a commercial maleated polyethylene (MAPE) was blended at various concentrations (0, 1, 3, 5, or 10 % w/w) with HDPE and a #50 sieved PWF fraction (containing 0, 25 or 50 % PWF w/w). Incorporation of high concentrations of MAPE (< 5 %) in HDPE-PWF blends improved tensile strength (TS) compared to lower MAPE concentrations (less than or equal to 3 %). Particle size of wood significantly influenced the mechanical properties of the resultant biocomposite. HDPE-MAPE blends containing smaller wood particles (less than or equal to #80) had higher TS than neat HDPE TS or blends containing larger particles (#40). Generally, Young’s modulus (YM) for all HDPE-PWF-MAPE blends was 50-70 % higher than that of neat HDPE. Generally, incubation of tensile bars of various HDPE-PWF blends in 95 % humidity for 28 d had little effect on their mechanical properties. Photo-spectra color analysis was employed to analysis the response of HDPE-PW composites to thermo-mechanical processing. Tensile bars from HDPE-PWF blends containing smaller particle sizes were significantly darker than blends containing larger particles. Differential scanning calorimetry (DSC) analysis showed differences in crystallinity and melting properties among the various HDPE-PW blends.